libfdt: Detected out-of-space with fdt_finish()

At present the Python sequential-write interface can produce an error when
it calls fdt_finish(), since this needs to add a terminating tag to the
end of the struct section.

Fix this by automatically expanding the buffer if needed.

Signed-off-by: Simon Glass <sjg@chromium.org>

scripts/dtc/pylibfdt/libfdt.i_shipped

@@ -786,7 +786,8 @@ class FdtSw(FdtRo):
             Fdt object allowing access to the newly created device tree
         """
         fdtsw = bytearray(self._fdt)
-        check_err(fdt_finish(fdtsw))
+        while self.check_space(fdt_finish(fdtsw)):
+            fdtsw = bytearray(self._fdt)
         return Fdt(fdtsw)
 
     def check_space(self, val):